Method and apparatus for drying a web

ABSTRACT

A method and apparatus for drying a web, moving in a generally convex arc of no more than 90*, by impinging air from a plenum on the concave side of the web, without contacting the convex side of the web with air jets or other support means. The efficiency of the plenum is increased by employing a plenum with a generally convex profile facing the concave side of the web and directing impinging air on the web from groups of air jet means positioned on the generally convex profile of the plenum. Intermediate adjacent air jet groups, there is positioned on the plenum supplemental air discharging means for directing air at the concave side of the web at a volume and speed different from that discharged by the air jet means to control the position of the web relative the air jet means.

United States Patent Continuation-impart of application Ser. No. 762,242, Sept. 16, 1968, now abandoned.

METHOD AND APPARATUS FOR DRYING A WEB 8 Claims, 4 Drawing Figs.

34/156 Int. Cl F26b 3/00 Field ofSearch 34/23,156

References Cited UNITED STATES PATENTS 3,048,383 8/1962 Champlih 34/156X 3,279,091 10/1966 Freuler 34/ l 56 Primary Examiner-Carroll B. Dority, Jr. Attorney-Walter O. Hodsdon ABSTRACT: A method and apparatus for drying a web, moving in a generally convex arc of no more than 90, by impinging air from a plenum on the concave side of the web, without contacting the convex side of the web with air jets or other support means. The efficiency of the plenum is increased by employing a plenum with a generally convex profile facing the concave side of the web and directing impinging air on the web from groups of air jet means positioned on the generally convex profile of the plenum Intermediate adjacent air jet groups, there is positioned on the plenum supplemental air discharging means for directing air at the concave side of the web at a volume and speed different from that discharged by the air jet means to control the position of the web relative the air jet means.

PATENIEDAuBmsn 3,599,341

' sum 2 UF 3 MIL TON P. DARCY JOSEPH N. TOML lNS'ON INVENTORS MMM A TTOR/VEY PATENTEUAUBHIQH 3599.341

SHEET 3 BF 3 ROOM A/R F REC/RCULATED All? MILTON PDARCY JOSEPH N. TOML/NSO/V INVENTORS A TTORNEY METHOD AND APPARATUS FOR DRYING A WEB CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 762,242 filed Sept. 16, 1968 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to an apparatus and method for drying a web. More particularly, the present invention relates to an apparatus and method for drying a web by employing an air-drying means adjacent to which the web, moving in a generally convex curved path, is passed.

In the art of drying a web coated with a wet material it is the customary procedure to move the web through an air-drying apparatus while supporting the web on a cushion of air so that the web does not contact objects until the coating is dry. A typical air dryer is simply an air box or plenum which has a plurality of orifices or tubes mounted on one side thereof. The plenum is supplied with a continuous stream of air which is distributed through the discharge orifices or tubes against the web. In some air-drying systems, the web is passed over a horizontal air dryer and streams of air are directed upwardly against the web to support and dry it. In other systems, the air dryer is oriented in a vertical direction and the web moves in a vertical path past the dryer, while dryingair, in the form of high-velocity airstreams, is directed against it.

In many cases, it is desirable to pass the web through either a vertical or horizontal air dryer having air discharge means oriented on opposite sides of the web. Such systems are desirable to effect a more rapid and efficient drying. However, in some cases, it is not desirable to dry both sides of the web simultaneously. This is particularly true where the material coated on the web is susceptible to disturbances from the high-velocity airstreams. The highvelocity air moving from the air dryers tends to distort and disturb the coating surface. It can be seen that difficult problems are encountered when the web cannot be supported and stabilized in a path between two airstreams. When the air is directed on the side of the web opposite the coated side and it is not desired to direct air against the coated side or place other restricting devices on that side, the web will tend to billow or move away from the air plenum.

As the web moves farther away from the air plenum, the effectivenessof the drying apparatus is greatly reduced. As the distance between the orifices or jets and the web increases, more drying time and air are required to properly dry the web or coating.

In some cases the billowing of the web can be controlled by tensioning devices which tend to hold and control the web path so that the web does not move away from the air plenum. However, many times the web material is not of the type that will withstand the tensions required to hold it in a stable path.

Therefore, in cases where it is not desirable to direct airstreams against both sides of the web or to overtension the web to hold it in a stable path, there is a need to provide a more effective drying apparatus.

There has long been a need for an air-drying apparatus which can dry a web on one side, yet can control and minimize the deflection between the web and the discharge orifice without overtensioning the web and without restricting the outward billowing movement with another airstream or other restrictive apparatus.

SUMMARY OF THE INVENTION The present invention is a method and apparatus for drying a web, moving in a generally convex arc of no more than 90 by impinging air on the concave side of the web without contacting the convex side of the web with air jets or other support means. The efficiency of the air drier is increased by employing a drier with a generally convex profile facing the concave side of the web and directing impinging air on the web from groups of air jet means positioned on the generally convex profile of the drier. Intermediate adjacent air groups, there is positioned onthe drier, supplemental air-discharging means for directing air at the concave side of the web at a volume and speed different from that discharged by the air jet means, to control the position of the web relative to the drier.

It is an object of this invention to provide a method and apparatus for drying a web which results in increased efficiency in the drying operation by controlling the position of the web relative to the drying air jet means.

This and other objects and advantages of the invention will become apparent from the following description taken in conjunction with the annexed drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side view of one embodiment incorporating the features of the present invention.

FIG. 2 is a fragmentary perspective view showing greater details of portions of the embodiment shown in FIG. 1.

FIG. 3 is a diagrammatic side view of another embodiment incorporating the features of the present invention.

FIG. '4 is a schematic diagram of the air supply for the apparatus shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, FIG. I shows one preferred embodiment of the drying apparatus into which the present invention has been incorporated. A web, W, to be dried is passed as a convex curve in spaced relationship to a side of main plenum 10, which has tube jets 14 positioned thereon for impinging drying air on the concave side of the web. As the web moves in a convex curved path, the total directional change of the web over the plenum side or the arc of the web adjacent the plenum side is no more than It should be appreciated that the convex curved shape of the web is caused by the air discharge directed at its plenum facing side.

The main plenum I0 is shown as a'hollow elongated box being curved along its longitudinal dimension. The plenum 10 has a curved tube sheet 12 to provide the plenum with a side having a generally convex profile facing the concave side of the web. The tube jets 14 are positioned on the convex profile of the plenum and they are arranged as groups 13, wherein adjacent groups are spaced from each other in the general direction of the web path. The plenum 10 is supplied with air through the pipes 16 which extend from an air supply source 17. The pipes 16 are connected to the plenum at several locations to distribute the air into plenum 10. Supplemental airdischarging means or air bars 18 are positioned intermediate adjacent air jet groups 13 and lie across the plenum 10. The air bars 18 are arranged transverse the longitudinal dimension of the plenum side and divide the plenum into air zones, each of which corresponds to a respective air jet group. The air distributed by the air bars 18 against the web, W, helps support the web as it passes over the plenum 10. i

In the embodiment shown in FIGS. 1 and 2, two such air bars 18 are positioned across the width of the plenum 10 at about the third points of the web span to divide the plenum 10 into three zones. The air bars 18 are hollow, elongated boxes having perforations 22 formed in the air discharge side 24. The air bars 18 are provided with a supply of air through pipes 26 from a source 28 which is independent of the supply to the plenum 10.

FIG. 2 shows a perspective view of a cross section of an air plenum 10 with an air bar 18 transversely disposed thereon. The plenum 10 is formed with a channel 30 extending transversely across the tube sheet so that an air bar I8 can be placed in the channel 30 as shown.

A second plenum 34, located downstream of plenum 10, is fabricated substantially identically with the main air plenum 10 and it too is a hollow elongated box being curved in its longitudinal dimension. The plenum has a curved tube sheet 36 i from which tube jets 38 are disposed.

The secondary plenum 34 is supplied with air through pipes 40 which convey the air from a supply source 42. The pipes 40 are connected to theplenum 34 at a number of locations to distribute the air to the plenum 34. In the embodiment as shown in FIG. 1, the second air plenum 34 has one air bar 44 disposed across the face of the tube sheet 36. This is because in the described embodiment the second plenum 34 is shorter than the main plenum l and fewer air bars are needed to support the web in a curved path.

The air bar 44 of the second plenum 34 is also supplied through pipes 45 with air from an air supply source 46 that is independent of the air source to the second plenum 34.

In the arrangement shown in FIG. 1, after the web passes over the main plenum 10, it passes over rollers 32 and then over the second plenum 34. The rollers can be power driven to assist in conveying the web over the main or second plenum. In the preferred embodiments the rollers 32 at both ends of the main plenum and at the end of the second plenum are power driven to assist in conveying the web.

An air reverser 50 is positioned adjacent the end of the second plenum 34. The reverser 50 is of a conventional design having its own air supply and is used for its intended purpose of changing the direction of travel of the web. After the web haspassed over the second plenum 34, it passes over the air reverser and then continues through the reminder of the webtreating apparatus (not shown).

As previously mentioned, the air supplies for the main plenum and the air bars 18 are separate and independent from one another. The same is true for the air supplies for the second plenum 34 and the air bar 44.

In the embodiment shown in FIG. 1 the airflow to the air bars and the plenum is provided by means of variably adjustable fans, 17, 28, 42, and 46. These fans are of conventional design having variable pitch blades so that the speed and volume of the air can be varied. Of course the air can be regulated by shutters and valves placed in the air supply line to the bars and plenums. This air can be heated if necessary by passing the air through suitable'heating device 52 of conventional construction. The air is heated after it passes through the fans 18 and 42.

It is important to the operation of the present invention that the air supply to the plenum be independent from the air supply to the air bars. This is so the speed and volume of both can be varied independent of the other. For example, when the drying conditions require that the tube jets be run with low speed air impinging on the web, the air from the air bars is of sufficient force to prevent the web from touching the tubes and to keep the web in a substantially curved path at an optimum distance from the plenum. When the air from the tube jets is impinged on the sheet at relatively high pressures, the airflow from the air bars may be reduced to reduce the deflection of the center of the web from the tube jet ends.

By varying the airflow from the air bars relative to the airflow from the tube jets, the distance of the web from the tube jets can be controlled and maintained at the desired level where the maximum effectiveness of the drying apparatus is realized.

With regard to the embodiment shown in FIGS. 3 and 4, there is shown an apparatus for drying a coated web, W. The web is dried by initially impinging air on only the uncoated surface without contacting the coated surface with air jets or other supporting means. A plenum 60 is employed which is tllvidcd by internal vertical bal'lle 67 into two portions 61 and 62. Plenum portion 61 has a web-facing side with a generally convex profile. On the profile there is disposed a plurality of tube jets or air jet means 64, which are arranged into groups 63. Intermediate adjacent groups 63 are supplemental airdischarging means or air bars 65 of similar construction to those shown in FIGS. I and 2.

The web to be dried is driven past plenum portion 61 by drive rollers 66 and is dried sufficiently, so that contact with both sides of the web may thereafter be made with low speed air. The web is then passed between plenum portions 62 and 71 of plenums and respectively. These plenum portions have perforated plated through which the drying air is discharged toward the web. About midway of the drying span of portion 62, there is positioned an air bar 68 for supporting the web during its slight change in direction. I

The web is thereafter turned 180 by an air reverser 73 and is further dried by air discharged from perforations in plenum portion 72 of plenum 70.

As was the case in FIG. 1, the billowing of the web adjacent plenum side 61 causes the web to take the form of an arc of less than 90.

The tube jets 64 are arranged into three groups, with adjacent groups spaced from each other in the general direction of the web path. group is characterized by having at least one point in the discharge surface of each of the tube jets in the group lying in a plane common to all of such points. In the embodiment shown in FIG. 3, adjacent groups have an obtuse angle defined between their respective planes. The profile of the planes being similar to a series of interconnected chords of a convex curve facing the concave side of the web.

In FIG. 4, fans 74, 75 and 76 are used to supply air under pressure to the various components of the drying apparatus. Recirculated air as well as room air is sent under pressure to heaters H and filters F, both of conventional design, and then to their respective discharge components which are schematically represented by numbered boxes corresponding to the parts in FIG. 3. Valves are employed at various points to permit flexibility in the amount of discharge from the component parts of the apparatus.

It can be seen that in this embodiment, the supply of air to the .air bars 65, 66 is independent of the air supply to the tube jets communicating with plenum portion 61. This permits the operator to vary the airflow from the air bars relative to the airflow from the tube jets so the distance of the web from the tube jets can be controlled to permit an increase in efiiciency for the drying operation.

It has been found that the optimum effectiveness of an air drier is realized when the distance between the web and the air discharge orifice is equal to approximately two times the orifice diameter. However, a range of between 2 to 4 diameters is acceptable. In the preferred embodiments the tube diameters are approximately 1 inch so that the effective distance between the web and tubes is 2 to 4 inches.

The key feature of the present invention can be more fully understood by comparing the present invention with a typical air drier in terms of optimum distance between the web and tube jets.

In a typical air-drying section wherein the web is dried from the back side, the web will billow out and move away from the air jets unless air is directed against the coated side or other restrictive devices are used to hold the web in position. The web can be held in place with contact bars, opposing air jets, or by tensioning the web so that it is not forced away from the tube jets. However, it may not be desirable to have the coated side contact a foreign body or for air to be impinged upon the coated surface. In addition, it may not be desirable to tension the web either because of the physical properties of the web or the condition of the coating.

In these cases, if the web cannot be restrained from moving away from the tube jets the distance between the tube jets and the web is increased and the effectiveness of the drier is greatly decreased.

We have found by allowing the web to billow out and by shaping the plenum to conform to the natural shape of the billowed web, and by controlling the air flow from the air bar relative to the airflow from the tube jets, that the web can be held in a position relative to the tubes, whereby the maximum effectiveness of the drier can be utilized.

When it is desired to increase the drying rate by impinging high-speed air on the web, further billowing of the web is lessened by having low-pressure air issuing from the air bars which are spaced at approximately the third points of the web span. The low pressure from the air bars flattens the slope of the curve of the web at the third points and this minimizes the total deflection of the web at the center of the span, resulting in a flatter curved web which is closer to the tube jets. Thus, by minimizing the maximum deflection of the web, the efficiency of the tube jet drier is improved.

Where the operation requires a relatively low speed of drying air from the tube jets, the air bars are adjusted to discharge high-speed air to support the web and prevent it from contacting the air jets.

in the preferred embodiments the air to the air bars is regulated relative to the air to the plenum depending upon the particular product being dried. The operator of the air-drying apparatus adjusts the flow of air from the air bars relative to the flow from the tube jets until the web is moving in a path at between 2 inches to 4 inches away from the tube jet ends. We have found for the normal spectrum of products that can be dried on apparatus incorporating the features of the present invention that an airflow to the tube jets not exceeding 100 cfm/ft of plenum area with a pressure drop of 2 inches of water across the plenum is usually the maximum flow required. For the air bars we have found that a maximum flow of 280 cfm/ft of plenum area with a pressure drop of 6 inches of water is usually the maximum flow required. Of course higher volumes and pressures could be used with the present invention, however, the piping system, plenums and air bars would have to be structurally stronger, resulting in higher costs. Furthermore, we have found that when drying thermoplastic webs and coatings that a maximum temperature of 300F. is usually satisfactory without changing the characteristics of the web and coating. However, if the product were such, then higher temperatures could be utilized.

The length of an individual plenum or the number of plenums and the number of air bars disposed across the plenums can vary depending upon the particular manufacturing problem. When a web or coating is difficult to dry, it may be necessary to pass the web over one or more additional spans of air-drying plenums. The converse is true with materials that are easily dried. in this case, a shorter plenum or fewer passes over plenum sections would probably be required to dry a web. This invention is applicable regardless of the length of a particular plenum or the number of plenums in an air-drying apparatus. Furthermore, conventional air driers could be placed in line after the second plenum if the additional drying were necessary. lf the coating on the web were sufficiently dry then restraining bars and air stream could be used to stabilize the web in a straight path.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. In a method for drying a web, moving in spaced relationship to a side of a plenum in a generally convex arc of no more than 90, by impinging air from said plenum on the concave side of said web, without contacting the convex side of said web with air jets or other support means, the improvement comprising the steps of:

employing a plenum wherein said side has a generally convex profile facing said concave side of said web;

directing impinging air on said concave side from groups of air jet means positioned on said generally convex profile, wherein adjacent groups are spaced from each other in the general direction of the web path;

and directing air at said concave side of said web, at a volume and speed different from that discharged by said air jet means, from supplemental air discharging means, positioned on said plenum intermediate adjacent groups of air jet means, to control the position of the web relative to said airjet means.

2. The invention according to claim 1 wherein said air jet means impinge high-pressure air on said web;

and said supplemental air-discharging means direct lowpressure air on said web at the third points of the web span to reduce the slope of said web at the third points and thereby reduce the deflection at the center of said web span.

3. The invention according to claim 1 wherein said air jet means impinge low-pressure air on said web;

and said supplemental air-discharging means direct highpressure air on said web to support said web and prevent said web from contacting said air jet means.

4. in an apparatus including a plenum for drying a web, moving in spaced relationship to a side of said plenum in a generally convex arc of no more than by impinging air from said plenum on the concave side of said web, without contacting the convex side of said web with air jets or other support means, and means for supplying drying air to said plenum, the improvement comprising:

said plenum having a side with a generally convex profile facing said concave side of said web; groups of air jet means positioned on said generally convex profile for directing impinging air on said concave side, said groups arranged so that adjacent groups are spaced from each other in the general direction of the web path;

and supplemental air-discharging means, positioned intermediate adjacent groups of air jet means and having an adjustable air supply means for directing an airflow against said concave side of said web with a volume and speed different from that discharged by said air jet means to control the position of said web relative to said air jet means.

5. The invention according to claim 4 wherein said air jet means are comprised of tubelike members mounted on said side of said plenum.

6. The invention according to claim 5 wherein said supple mental air-discharging means are comprised of hollow elongated boxes having perforations for discharging air toward said web.

7. The invention according to claim 6 wherein said supplemental air-discharging means are positioned at about a one third and a two third points of said convex arc.

8. An air impingement drying apparatus for drying a web by impinging air on only one side thereof, without contacting the other side with air jets or other supporting means, while said web moves in spaced relationship to a side of said apparatus in a generally convex arc of no more than 90, said apparatus comprising:

groups of air jet means positioned on said side of said apparatus for impinging drying air on said one side of said web, a group characterized by having at least one point in the discharge surface of each of the air jet means in the group lying in a plane common to all of such points, said groups facing said one side of said web and positioned so that adjacent groups are spaced from each other in the general direction of the web path and wherein said adjacent groups respective planes have an obtuse angle defined therebetween, the profile of said planes being similar to a series of interconnected chords of a convex curve facing said one side of said web;

means for supplying drying air to said airjet means;

and supplemental air-discharging means positioned intermediate adjacent groups of air jet means and having an adjustable air supply means for directing an airflow against said one side of said web with a volume and speed different from that discharged by said air jet means to control the position of the web relative to saidair jet v means. 

2. The invention according to claim 1 wherein said air jet means impinge high-pressure air on said web; and said supplemental air-discharging means direct low-pressure air on said web at the third points of the web span to reduce the slope of said web at the third points and thereby reduce the deflection at the center of said web span.
 3. The invention according to claim 1 wherein said air jet means impinge low-pressure air on said web; and said supplemental air-discharging means direct high-pressure air on said web to support said web and prevent said web from contacting said air jet means.
 4. In an apparatus including a plenum for drying a web, moving in spaced relationship to a side of said plenum in a generally convex arc of no more than 90*, by impinging air from said plenum on the concave side of said web, without contacting the convex side of said web with air jets or other support means, and means for supplying drying air to said plenum, the improvement comprising: said plenum having a side with a generally convex profile facing said concave side of said web; groups of air jet means positioned on said generally convex profile for directing impinging air on said concave side, said groups arranged so that adjacent groups are spaced from each other in the general direction of the web path; and supplemental air-discharging means, positioned intermediate adjacent groups of air jet means and having an adjustable air supply means for directing an airflow against said concave side of said web with a volume and speed different from that discharged by said air jet means to control the position of said web relative to said air jet means.
 5. The invention according to claim 4 wherein said air jet means are comprised of tubelike members mounted on said side of said plenum.
 6. The invention according to claim 5 wherein said supplemental air-discharging means are comprised of hollow elongated boxes having perforations for discharging air toward said web.
 7. The invention according to claim 6 wherein said supplemental air-discharging means are positioned at about a one third and a two third points of said convex arc.
 8. An air impingement drying apparatus for drying a web by impinging air on only one side thereof, without contacting the other side with air jets or other supportiNg means, while said web moves in spaced relationship to a side of said apparatus in a generally convex arc of no more than 90*, said apparatus comprising: groups of air jet means positioned on said side of said apparatus for impinging drying air on said one side of said web, a group characterized by having at least one point in the discharge surface of each of the air jet means in the group lying in a plane common to all of such points, said groups facing said one side of said web and positioned so that adjacent groups are spaced from each other in the general direction of the web path and wherein said adjacent groups'' respective planes have an obtuse angle defined therebetween, the profile of said planes being similar to a series of interconnected chords of a convex curve facing said one side of said web; means for supplying drying air to said air jet means; and supplemental air-discharging means positioned intermediate adjacent groups of air jet means and having an adjustable air supply means for directing an airflow against said one side of said web with a volume and speed different from that discharged by said air jet means to control the position of the web relative to said air jet means. 